Technical Field
The present invention relates to an imaging optical system, a camera apparatus, and a stereo camera apparatus.
Description of Related Art
As camera apparatuses including imaging optical systems and area sensors, monitoring cameras, vehicle-mounted cameras, and the like are practically being used. These cameras are used for sensing purpose, i.e., to identify an object. For instance a vehicle-mounted camera is used to identify a position of the traveling vehicle, a road condition, and the like.
Here, the imaging optical systems for sensing purpose must have a high resolution so as to identify relatively a small object or to monitor a condition of an object from a relatively long distance.
As imaging optical systems provided to camera apparatuses for sensing purpose, retrofocus-type imaging optical systems are taught by PTL1 (JP2006-309076A), PTL2 (JP2004-341376A), and PTL3 (JP2012-220741A). The image optical systems of the PTLs 1 to 3 have a front lens group with a negative power on the object side and a rear lens group with a positive power on the image side (i.e., the front lens group and the rear lens group are aligned in an asymmetrical manner). As a result, the camera secures an enough space to dispose filters such as an optical low pass filter and an infrared cut filter between the optical system and the image sensors, thereby achieving an appropriate optical performance for sensing.
Further, the optical systems for sensing purpose are required to accurately identify the sizes, shapes, and the like of the objects. Hence, the distortion aberrations must appropriately be corrected even for wide angle cameras. Therefore, it is desirable to develop an imaging optical system that can reduce distortions, thereby achieving low distortion.